As an on-vehicle lithium ion battery, a cylindrical or square sealed type battery is used. While many cylindrical batteries had been used, more square batteries have been used in these days in view of improvement in a mounting density for vehicle use. A square battery and a battery pack including a plurality of square batteries combined are demanded to be small-sized and light-weighted and many attempts have been accordingly made to reduce a plate thickness of a battery can.
Many of square batteries use a metallic battery can of a rectangular solid shape whose opening portion has a larger depth dimension than a shorter side dimension obtained by deep drawing or the like. In the rectangular solid-shaped battery can, a flat wound group is housed with an insulation sheet provided therebetween.
The flat wound group includes a positive electrode plate and a negative electrode plate each having a current collecting foil overlapped and wound or a plurality of them laminated alternately, in which at both ends, a part not coated with a positive electrode active material mixture and a part not coated with a negative electrode active material mixture are separately arranged. To each of the uncoated parts, a pole plate is joined by ultrasonic bonding or the like. The opening portion of the battery can is sealed by a metallic battery lid. To the battery lid, a positive electrode terminal and a negative electrode terminal for the connection with an external load are fixed via a gasket for providing electrical insulation from the battery lid and maintaining airtightness of the inside of the battery. The battery lid is welded to the battery can by laser beam welding or the like to seal the opening portion of the battery can.
In a square battery of PTL 1, a battery can and a battery lid are fillet welded by laser to configure a battery container. Specifically, the battery lid is provided with a fit-in portion to be fit in an opening portion of the battery can, and a flange portion in contact with an upper end surface of the opening portion of the battery can, and with the fit-in portion fit in the opening portion, the battery lid is fixed by fillet welding the flange portion to the upper end surface of the opening portion of the battery can on both sides of the wide side surface and the narrow side surface.